This invention is directed to a spreading apparatus for granular material and more specifically to a broadcast spreading apparatus capable of laying down on a field a uniform pattern of fertilizer or other ground conditioning materials at a uniform density to promote optimum growth and highest yield in crops subsequently raised on these fields.
Many fan type centrifugal spreaders of the past, which are arranged to be towed by a tractor along the surface upon which the fertilizer is to be applied, have been provided with feed conveyors which are driven by a power take-off means from the tractor or by a driver wheel associated with one of the spreader's ground support wheels in order to deliver a proportional quantity of fertilizer to the spreading fan which is consistant with the towed speed of the spreading apparatus. The spreading fans are also directly driven by the same power source and are arranged to rotate at a speed to provide a preferred spreading pattern of fertilizer when the spreading apparatus moves along the field at an ideal rate of speed. Frequently, however, this ideal speed cannot be maintained, as for example with hilly ground, obstructions, etc., resulting in substantial variations in the conveyor and spreading fans speeds. Thus, while fertilizer will be delivered to the spreading fan at desirable volumes, despite towing speed variations, variation in the spreading fan rotational speed significantly alters the spreading pattern width of fertilizer layed down on a field. With adjacent patterns of fertilizer subject to similar variations in coverage a considerable area will be either overlapped and accordingly overfertilized, or will be missed altogether with no fertilizer spread on these areas.
Overfertilization, apart from being wasteful, results in excess stem growth with accompanying stem weakness. Herein, as for example with grain, the heads will often lay over or collapse to the ground, especially when subjected to adverse weather conditions, making this grain difficult if not impossible to harvest. Further, grain or other crops which were planted in the areas of no fertilization would produce a poor yield.
To overcome this problem, some spreaders in the past were provided with an independent power source such as an internal combustion engine to drive the feed conveyors and spreading fans. This arrangement adds considerably to the cost and operation of the spreaders. These machines also require transmissions and gear reducers to provide suitable speed controls for the conveyor and the spreader fans with an operator needed to make suitable adjustments from time to time to match the towing speed of the spreader unit. Thus, while the towing speed of the spreader unit will not affect the spreading pattern widths, adjustments must be made to match the conveyor speed (fertilizer delivered to the spreader fan) with the towed speed of the spreader unit if uniform coverage is to obtained.
Accordingly, a spreader which could continuously proportion the flow of fertilizer delivered to the spreading fans based on the towing speed of the spreading apparatus, yet distribute this proportioned quantity of fertilizer over a uniform area of a field, would be a decided advance in the state of the art.